1. Field of the Invention
The present invention generally relates to a combustion knock preventing apparatus for internal combustion engine. More specifically, the present invention relates to an improvement in a combustion knock preventing apparatus which retards the ignition timing to decrease the occurrence of the combustion knock in an internal combustion engine in response to a monitoring signal produced by a knock sensor.
2. Description of the Prior Art
Combustion knock of an internal combustion engine occurs when the ignition timing is too far advanced and a high load is put on the engine. It is well known that continued engine operation under a high intensity of combustion knock results in damage to the engine. However, it is also well known that an optimum engine output performance and fuel consumption characteristics are obtained when it is operated under a slight knock condition.
There is a close relationship between the ignition timing and the occurrence of combustion knock. Generally, the combustion knock increases as the degree of the advancement of the ignition timing increases.
As the ignition timing is advanced up to the point where the combustion knock occurs, retarding the engine timing is effective to prevent too much combustion knock. In some conventional combustion knock preventing apparatuses, there are provided a sensor monitoring the combustion knock condition, and an ignition timing controller for retarding the ignition timing when the engine knocks too much so as to maintain the engine operation under a slight knock condition, thereby improving the engine output performance and the fuel consumption characteristics.
The sensor generally comprises a vibration sensor connected to the engine cylinder head for converting the vibration caused by the combustion knock into an electric signal. The output signal of the vibration sensor is compared with a reference signal to produce an output signal for actuating the ignition timing controller.
However, if the ignition timing controller receives a false knock detection signal at low engine speed, as when the battery power is too low to produce an accurate reference signal, it will automatically retard the ignition timing. When this happens, the engine may stall. Similarly, if this happens during engine cranking operation, it may make the engine difficult to start.